Green’s Dictionary of Slang

rapper n.1

[SE rap, a blow]

a major lie.

[UK]Dialogue between a Yorkshire Alderman and a Salamanca Doctor 2: At Langhorns Tryal, thou swor’st thou saw’st him Forty times in July following, that was a Rapper.
[UK]B.E. Dict. Canting Crew n.p.: Rapper a swinging great Lie.
[UK]New Canting Dict. [as cit. c.1698].
[UK]Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
[UK]Grose Classical Dict. of the Vulgar Tongue.
[UK]Lex. Balatronicum.
[UK]Egan Grose’s Classical Dict. of the Vulgar Tongue.
[UK]Duncombe New and Improved Flash Dict. n.p.: Rapper a bouncing lie.